Cytogenetic analysis is an important diagnostic laboratory tool in medical genetics, oncology, and genetic research. Nearly one in every 150 newborns is affected with a chromosome defect that requires analysis and evaluation by a clinical cytogenetics service. An equivalent caseload comes from both hematologic and solid tumors that are evaluated cytogenetically as a routine part of cancer diagnosis. Historically, cytogenetic analysis has been performed by specially trained technologists and professionals with specific expertise in a variety of chromosome banding methods and their interpretation. However, with the increasing awareness of the value of cytogenetic assessment in both clinical medicine and in research, there is both a shortage of qualified cytogeneticists and an increased need for rapid and definitive diagnostic assays. The current Phase I proposal aims to significantly improve the existing technology by: (1) evaluating rapid methods of generating chromosome- specific DNA probes for use in fluorescence in situ hybridization assays; and (2) testing several new approaches to probe labelling that will both enhance the performance of fluorescence assays by adding routine detection of multiple chromosomes labelled with different colors and significantly reduce the time required for detection of labelled probes.